Some tasks of observational gamma-ray astronomy in the energy range 5?400 GeV

Abstract

Brief discussion of the necessity to carry out gamma-ray observations in the uninvestigated energy range 5-400 GeV by instrument on the board of space vehicle is given. One of the possible versions of such gamma-telescope is described and some estimations of the possible statistics are made. State of Observations in Gamma-Ray AstronomyObservations of celestial gamma-radiation cover a wide energy range: from the lowest energies that are still called ~,-rays (hundreds of keV) up to approximately 1016 eV. In the energy range from 50-70 MeV up to GeV the main information about gammaradiation was so far obtained with the satellites SAS-2 (Fichtel et al., 1975) and COS-B (Bignami et al., 1982). In the range 1012-1016 eV detection of the ~,-quanta is performed with ground instruments measuring Cerenkov radiation of extensive air shower (EAS) particles or of charged components of the EAS generated by the primary y-quanta in the atmosphere (see the Review by Vladimirsky et al., 1985). But up to now there have been no 7-ray experiments in the 4-400 GeV energy range, although this interval is of great interest for solving the problem of the origin of the y-radiation.One can describe the energy spectrum of the diffuse gamma-radiation of the Galaxy in the energy range from 0.01 MeV up to 3-4 GeV (for galactic latitudes _+ 10 ~ by the function I(Er) dE~ = AE] n dE 7 with n ~ 1.9 (see Figure 1 and Sacher et al., 1983). According to modern ideas the diffuse y-radiation of the Galaxy at E~ > 0.1 GeV is the result of the decay of n~ generated by primary cosmic-ray protons and nuclei in the process of their interaction with interstellar gas in the galactic disk. In this case the energy spectrum of the 7-radiation must reflect the proton spectrum and consequently have n ~ 2.7. The difference between the observed and expected y-spectrum shapes in the energy range below 4 GeV is possibly connected with the proximity of this energy region to the threshold of n~ formation and the E-27 dependence will occur only at higher energies. That can be discovered if one carries out observations in the energy range 1-400 GeV.It is known that at present about 25 discrete y-sources have been discovered. Their energy spectra are defined only for the most intense sources or for those having some peculiar characteristics. Let us list some data for 4 of them.

High-energy gamma-ray studying with GAMMA-400

“…2 THE GAMMA-400 GAMMA-RAY TELESCOPE Thus, to resolve unidentified gamma-ray sources and search for the potential gamma-ray lines from DM we need a gamma-ray telescope with the angular resolution of several hundredth degrees and the energy resolution of few percent for the energy of ~100 GeV. Such a new generation telescope will be GAMMA-400, which will be installed onboard the Russian space observatory [15][16][17][18][19][20].…”

GAMMA-400 gamma-ray observatory

“…This task was set for the GAMMA-400 project by Nobel Laureate Academician V.L. Ginzburg in the end of 1980's [1,2] and his list of very important issues in modern cosmology at the beginning of XXI Century noted the issue of dark matter and its detection [3]. Within the framework of this project, which has now since expanded internationally, the design and construction of a future, complex, precision gamma-ray telescope is being carried out [4][5][6][7].…”

Status of the GAMMA-400 project

“…1. The basic idea of the instrument was outlined in earlier publications (Dogiel et al, 1988, Ginzburg et al, 2007, but the design is being improved (Galper et al, 2011a(Galper et al, , 2011b(Galper et al, , 2011c using the results of the current space missions Fermi-LAT and AGILE. Gamma-400 consists of scintillation anticoincidence top and lateral detectors (AC), converter-tracker (C) with approximately 25 layers of double (x, y) silicon strip coordinate detectors (pitch 0.1 mm) interleaved with tungsten conversion foils, scintillation detectors (S1 and S2) of time-of-flight system (TOF), silicon strip coordinate detector CD1 (pitch 0.1 mm), scintillation detectors S3 and S4, silicon arrays (silicon pad detectors with 1×1 cm 2 pixels), lateral detectors (LD) from the same Si arrays and tungsten planes, and calorimeter from two parts (CC1 and CC2).…”